The development of wound infection is a problem for many patients. Infected wounds can cause distress from associated morbidity and mortality, increased length of hospital admission, delayed wound healing and increased discomfort. Early recognition of the signs of infection, local swelling, heat, pain and redness, followed by effective intervention, is necessary to achieve prompt resolution. Infected wounds frequently have increased levels of exudate, pus and odour, and the patient might be pyrexial and/or have an elevated neutrophil count.
In clinical practice, a diagnosis of infection is based on the presence of the above symptoms, although many clinical indicators, such as inflammation and discharge, have a low predictive value of infection in wounds. Definitive diagnosis is achieved by microbiological analysis of wound samples. Tissue biopsy provides the most accurate results, but this is an invasive procedure that is difficult to achieve for the mass of specimens required. Wound swabbing is the most common wound sampling method used throughout the UK although its clinical value has been questioned. Furthermore, microbiological diagnosis of wound infection can take 48 to 72 hours, which allows time for infection to further develop if first-line/best-guess treatment is not employed immediately.
There therefore remains a need in the art for a method for the early diagnosis and prognosis of wound infection, and for devices and wound dressings for use in carrying out such methods.
Concentrations of reactive oxygen species (ROS) are known to rise in damaged tissues, producing a condition known as oxidative stress. ROS generation by inflammatory cells within the dermis play an important role in mediating wound healing. However, prolonged and more severe oxidative stress may delay healing because it will produce chronic inflammation, divert available energy supply towards antioxidant defence at the expense of tissue reconstruction, and increase levels of matrix metalloproteinases which cause tissue breakdown. A variety of cellular (enzymatic) and extracellular (non-enzymatic) antioxidant entities exist within normal and inflamed dermal tissues and fluids to counteract the direct effects of ROS by direct scavenging and by sequestering free transition metal ions.
It has been reported that the antioxidant activity of healing wounds is not significantly higher than that of non healing wounds. Recent evidence indicates that there is no significant difference in the total antioxidant capacity of acute and chronic wound fluid, although chronic wound fluid exhibited higher total antioxidant capacity when variations in wound fluid protein content were accounted for (Moseley et al., (2004) Wound Repair and Regeneration vol. 12, No. 4, 419-429).